This invention relates to a communications system, and more particularly to a local area network (LAN), and a discriminator for detecting the type of coupling utilized in signal driver circuits supplying signals between a station and the LAN.
Stations of a LAN may include interactive workstations such as personal computers and word processors, as well as passive devices comprising data stores, printers, video display terminals, etc., all of which can have substantial data processing capabilities. Current trends are toward sharing data among these stations, not only for implementing data and document communication and distributed processing applications, but also to allow workstations to share the more expensive system components, viz.: those having mechanical elements and/or moving media such as printers and secondary disk storage devices.
Local area networks comprise data communications systems which interconnect computers, peripherals, video display terminals and other devices dispersed over a limited geographical area, e.g., within a building or throughout a cluster of buildings. LANs typically transfer data at rates in the range of 1-10 million bits per second. However, the numbers are arbitrary, and the boundary between the high end of a LAN and the low end of a large topology network is determined more by the data rate and organization of the network than by its geographical dispersion. Local networks are generally characterized by inexpensive transmission media and modems, but high data rates compared with those of the traditional voice-grade telephone system. Transmission media most commonly used in LANs are coaxial cable and twisted-pair wiring.
Research and development of local area networks began in the early 1970s, but industry standards for LANs and LAN equipment are only now being developed by standards groups such as the European Computer Manufacturers Association (ECMA), the Institute of Electrical and Electronic Engineers (IEEE), and various industry groups. Consequently, there are a variety of system approaches to LANs, and more than 250 vendors of networks and network components. Some of the vendors offer open systems allowing interconnection of products from more than one vendor, while others provide closed systems which makes it difficult to connect various types of equipment to the system. Therefore, interface components, which connect stations to the LAN, may not be compatible with a particular LAN system. Incompatibilities between system components are usually resolved by providing multiple circuits in the interface equipment, one for each operating configuration, requiring strapping options for manually selecting the proper circuit. The use of such strapping options necessitates determination of the system or interface configuration by a technically qualified person and then the strap must be installed or changed manually. It is desirable that stations such as personal computers, data terminals, etc., be connectable to a LAN system without the assistance of technical personnel.
It is therefore an object of the invention to provide an improved interface circuit for local area network equipment.
It is another object of the invention to provide an improved coupling discriminator for an interface transceiver in a local area network.
It is another object of the invention to provide an improved coupling discriminator in an Ethernet local area network.